ARS | Publication request: Multiparasitism by Tetrastichus planipennisi (Hymenoptera: Eulophidae) and Spathius agrili (Hymenoptera:Braconidae): Implication for biological control of the Emerald Ash Borer Larvae (Coleoptera: Buprestidae)

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 26, 2012
Publication Date: N/A

Interpretive Summary: The emerald ash borer (EAB) is a devastating forest pest in North America, killing hundreds of millions of native North American ash (Fraxinus spp.) trees since its discovery in Michigan, USA in 2002. Two species of parasitic wasp (Tetrastichus planipennisi and Spathius agrili) were recently introduced from the pest’s native home (China), and released against EAB in the north central and northeastern United States. Because both species of parasitic wasps attack the similar larval stages of EAB, however, the potential exists for competition between these two parasitoids. We conducted laboratory experiments to examine the potential interactions between these two parasitic wasps when they compete for the same EAB host larvae. Results from our study showed that the parasitic wasp T. planipennisi attacked EAB larvae already parasitized by the other parasitic wasp (S. agrili) for up to 2 days, but not 4 days. However, parasitism rates were significantly lower in previously parasitized hosts as compared to healthy EAB larvae. These results suggest that competitive interactions between these parasitoids would be of limited importance on the biological control program if these species were released against EAB at the same time and place.

Technical Abstract: Interspecific competition among different species of insect parasitoids may affect the establishment or efficacies of these species in biological control of targeted pests. The endoparasitoid Tetrastichus planipennisi Yang and the ectoparasitoid Spathius agrili Yang, two gregarious larval parasitoids native to China, have recently been introduced to the United Sates for biological control of emerald ash borer (EAB), Agrilus planipennis Fairmaire. The potential interspecific competition between these two parasitoids via multiparasitism of the same host larva was examined in laboratory. In dual choice-assays where healthy EAB larvae were presented along with those already parasitized by S. agrili at different times, T. planipennisi attacked hosts parasitized by S. agrili for up to 2 days, but not 4 days. Compared to healthy EAB larvae, the parasitism rate was not significantly different in the hosts previously parasitized for 0 days, but decreased significantly in those for 2 days. This indicates that the ability of T. planipennisi to discriminate host larvae parasitized by S. agrili increased significantly two days after the host larvae parasitized by S. agrili. Additional observations showed that a majority (> 91%) of EAB larvae parasitized by S. agrili were completely paralyzed two day after the attack, indicating that paralyzation of host larvae by S. agrili allows T. planipennisi to discriminate between healthy and previously parasitized larvae. In no-choice assays where T. planipennisi females were presented either with healthy EAB larvae or EAB larvae exposed to S. agrili at 0, 2 and 4 days earlier, T. planipennisi parasitized significantly more healthy EAB larvae than S. agrili -parasitized larvae in all the exposure times. In addition, the subsequent attack by T. planipennisi did not affect either parasitism rates by or progeny production of S. agrili, irrespective of the duration between S. agrili and T. planipennisi exposures. These results suggest that competitive interactions between these parasitoids would be of limited importance on the biological control program if these species were released against EAB at the same time and place.